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refrigerant shall be recovered from the system, or isolated (by means of
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shut off valves) in a part of the system remote from the leak. Oxygen free
nitrogen (OFN) shall then be purged through the system both before and
during the brazing process.
Removal and evacuation
When breaking into the refrigerant circuit to make repairs – or for any
other purpose – conventional procedures shall be used. However, it is
important that best practice is followed since flammability is a
consideration. The following procedure shall be adhered to:
• remove refrigerant;
• purge the circuit with inert gas;
• evacuate;
• purge again with inert gas;
• open the circuit by cutting or brazing.
The refrigerant charge shall be recovered into the correct recovery
cylinders. The system shall be "flushed" with OFN to render the unit safe.
This process may need to be repeated several times. Compressed air or
oxygen shall not be used for this task.
Flushing shall be achieved by breaking the vacuum in the system with OFN
and continuing to fill until the working pressure is achieved, then venting to
atmosphere, and finally pulling down to a vacuum. This process shall be
repeated until no refrigerant is within the system. When the final OFN
charge is used, the system shall be vented down to atmospheric pressure to
enable work to take place. This operation is absolutely vital if brazing
operations on the pipe-work are to take place.
Ensure that the outlet for the vacuum pump is not close to any ignition
sources and there is ventilation available.
Charging procedures
In addition to conventional charging procedures, the following
requirements shall be followed.
– Ensure that contamination of different refrigerants does not occur when
using charging equipment. Hoses or lines shall be as short as possible to
minimise the amount of refrigerant contained in them.
– Cylinders shall be kept upright.
– Ensure that the refrigeration system is earthed prior to charging the
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